The invention relates to phase and frequency-locked loop circuits (PLL and FLL circuits).
PLL and FLL circuits are at present finding a plurality of applications in electronic circuits for the purpose of synchronizing a frequency-controllable tracking oscillator (usually a voltage-controlled oscillator [VCO]) in either phase or frequency with the signal of a reference oscillator (such as a crystal-controlled oscillator), whose phase or frequency, respectively, is virtually constant in comparison with the voltage-controlled oscillator. The clock frequency generated by the tracking oscillator is thereby greater by a certain factor (such as 100) than the frequency of the reference oscillator, and is applied, via a frequency divider, to a phase or frequency comparator, respectively, which generates the signal for the control of the tracking oscillator. The output signal generated by the tracking oscillator can then, for example, be used as the system clock signal for a microprocessor.
Apart from the PLL and/or FLL circuits, nowadays a plurality of further circuit components, to fulfill a variety of functions, are generally also integrated on the same chip. These may, for example, include circuit components for the measurement of certain parameters, such as the ambient temperature or a changing supply voltage, and which make this information available to other circuit components for whose functioning this information is of significance.
The micro-electronics industry is constantly striving to make the best possible use of the space that is available on a microchip for the sum of the plurality of circuit components, and to reduce the size of these circuit components to the greatest possible extent. This requirement has not been met in the best possible way in previous circuits containing both a PLL or an FLL circuit, as well as circuits for the measurement of temperature and/or voltage, respectively.
The purpose of the present invention therefore is to provide a PLL or FLL circuit, respectively, in conjunction with a circuit for the measurement of specific parameters (such as temperature or supply voltage), that will use less circuit space than previous embodiment solutions, and that can also be produced more cost effectively.
This requirement is met by a phase-locked loop circuit (PLL circuit) in conjunction with a controllable tracking oscillator whose signal phase relationship is influenced by an external parameter, a reference oscillator whose signal phase relationship is constant, as well as a phase comparator to compare the phase relationship of the signal supplied by the tracking oscillator with the phase relationship of the signal supplied by the reference oscillator, and which supplies an output signal characteristic of the phase shift to the tracking oscillator, with which this will be controlled in such a way that phase errors are reduced, and where furthermore an element for the monitoring of the external parameter is provided which is conceived in such a way that it can receive a signal representing the output signal characteristic of the phase shift, and so change it into a measured value which represents the real value of the external parameter.
Furthermore, this requirement is also met by the use of a frequency-locked loop circuit (FLL circuit) in conjunction with a controllable tracking oscillator whose frequency is influenced by an external parameter, a reference oscillator whose frequency is constant, as well as a frequency comparator which compares the frequency of the signal supplied by the tracking oscillator with the frequency of the signal supplied by the reference oscillator, and which supplies an output signal characteristic of the frequency difference to the tracking oscillator, with which this will be controlled in such a way that frequency errors are reduced, and where furthermore an element for the monitoring of the external parameter is provided which is conceived in such a way that it can receive a signal representing the output signal characterizing the frequency shift, and so change it into a measured value which represents the real value of the external parameter.
The invention makes use of the fact that the level of the signal output by the phase/frequency comparator during the operation of a PLL or FLL control circuit, when the frequency of the tracking synchronizer is influenced by only one external parameter, such as the ambient temperature, characterizes this parameter, so that the measured value of the parameter, such as the ambient temperature, can be determined from this with the help of one further element. The invention therefore integrates the previously used circuit components for the parameter determination into the PLL or FLL circuit itself and thereby both reduces production costs as well as the requirement for circuit space as compared with conventional solutions.
The element used to measure the external parameter thereby preferably includes a microprocessor. If the tracking oscillator is used to supply the clock pulses for the microprocessor, there will be no need for any further circuit components to achieve phase or frequency tracking, as well as the determination of parameters, as compared with existing conventional methods. Advantageous further developments of the invention are designated in the subclaims.